Polyoxyalkylene-modified organopolysiloxanes, which are a type of polyether-modified organopolysiloxanes, have heretofore been produced by a hydrosilylation reaction in the presence of a hydrosilylation reaction catalyst (e.g., chloroplatinic acid) between silicon-bonded hydrogen atom-functional organopolysiloxane and polyoxyalkylene bearing an aliphatically unsaturated group (e.g., allyl group) in terminal position. However, it is known that polyoxyalkylene-modified organopolysiloxanes (i.e., a type of polyether-modified organopolysiloxanes) produced in this manner are readily susceptible to oxidation in the presence of air and that allergenically antigenic oxidation products, e.g., formaldehyde, other aldehydes, formate esters, and so forth, are thereby produced with elapsed time in storage.
The established theory for the mechanism underlying this aldehyde production is as follows. When a hydrosilylation reaction is carried out between an organopolysiloxane containing silicon-bonded hydrogen atoms and an aliphatically unsaturated group (e.g., allyl)-terminated polyoxyalkylene in the presence of a platinum catalyst using a polyoxyalkylene monoallyl ether as the aliphatically unsaturated group (e.g., allyl)-terminated polyoxyalkylene, the allyl group undergoes an internal rearrangement in a secondary reaction to produce the polyoxyalkylene mono-1-propenyl ether. This polyoxyalkylene mono-1-propenyl ether, however, is refractory to reaction with the organopolysiloxane containing silicon-bonded hydrogen atoms.
Due to this, it remains as an impurity, along with unreacted polyoxyalkylene monoallyl ether, in the polyoxyalkylene-modified organopolysiloxane produced by the normal hydrosilylation reaction. The unreacted polyoxyalkylene monoallyl ether is gradually isomerized under the action of the residual platinum catalyst into polyoxyalkylene mono-1-propenyl ether.
The ether linkage is cleaved when water acts on the polyoxyalkylene-modified organopolysiloxane containing these impurities, resulting in the production of propionaldehyde and the generation of undesirable odor. This reaction is accelerated by the presence of acid, and its reaction rate rises as the pH declines.
U.S. Pat. No. 5,225,509 and Japanese Unexamined Patent Application Publication No. Hei 07-330907 (JP H07-330907 A) disclose a method in which alkylation is carried out by the hydrogenation of residual unsaturated double bonds. It is reported that this method eliminates the unsaturated bonds in a polyoxyalkylene monoallyl ether and polyoxyalkylene monopropenyl ether, and that as a consequence odor substances such as aldehydes are substantially not produced and an odor-free polyoxyalkylene-modified organopolysiloxane can be produced.
Japanese Patent No. 2,137,062 reports that, based on the elucidation of the odor mechanism cited above, the removal of odor substances produced by subjecting a polyoxyalkylene-modified organopolysiloxane containing the aforementioned impurities to treatment under prescribed conditions with water and an aqueous solution having a pH of 7 or less until the degree of unsaturation originating in the residual double-containing polyoxyalkylene in the copolymer reaches to 0.002 or less can yield a polysiloxane-polyoxyalkylene copolymer that does not produce undesirable odor with elapsed time.
These production methods can produce the odor-free polyoxyalkylene-modified organopolysiloxane that does not contain carbonyl-functional allergenically antigenic compounds such as aldehydes. However, they cannot prevent the production of carbonyl-functional allergenically antigenic compounds (typified by formaldehyde) during post-production storage. This is due to the fact that the polyoxyalkylene chain itself is quite susceptible to oxidation.
It has been reported in, for example, Acta Dermato-Venereologica, 79, 5-26 (1999); J. Pharm. Sci., 87, 276 (1998); Contact Dermatitis, 44, 207 (2001); Contact Dermatitis, 39, 14 (1998); J. Pharm. Sci., 88, 4 (1999); and Contact Dermatitis, 44, 207-212 (2001) that the polyoxyalkylenes undergo oxidative degradation in the presence of air to give various carbonyl-functional allergenically antigenic compounds, and hence the oxidative degradation of the silicon-bonded polyoxyalkylene chains in polyoxyalkylene-modified organopolysiloxanes is also unavoidable.    [Patent Reference 1] U.S. Pat. No. 5,225,509    [Patent Reference 2] Japanese Unexamined Patent Application Publication No. Hei 07-330907    [Patent Reference 3] Japanese Patent No. 2,137,062    [Nonpatent Reference 1] Acta Dermato-Venereologica, 79, 5-26 (1999)    [Nonpatent Reference 2] Pharm. Sci., 87, 276 (1998); Contact Dermatitis, 44, 207 (2001)    [Nonpatent Reference 3] Contact Dermatitis, 39, 14 (1998); J. Pharm. Sci.     [Nonpatent Reference 4] Contact Dermatitis, 44, 207-212 (2001)